The invention relates to a method for cyclically shielding a work chamber opening when loading and unloading workpieces as well as a shielding device for carrying out the method.
Work chambers are used for the treatment of workpieces, in particular for surface treatment with abrasive or surface-compacting particles, in order to protect the surroundings from the blasting agents flying about. The workpieces are transported into the work chamber through an opening in the work chamber wall. The opening is then closed and the blasting agent is blasted onto the workpiece using turbine wheels or pneumatic blasting agent nozzles. The disadvantages of such a discontinuous method are the required set-up times for stopping the blasting agent supply, opening the work chamber opening, moving the workpiece in and closing the work chamber opening and re-starting the blasting agent supply and the treatment process. Such a method is uneconomical especially for large numbers of small workpieces.
It is also known to place workpieces on a cyclically movable, in particular a round, feeding device that loads the workpiece into the work chamber through a first opening and unloads it from there through an additional opening. The advantage is that the workpiece can be already placed onto the exterior portion of the conveyor device outside the work chamber while the treatment of other workpieces is still in progress inside the working chamber. The workpieces that have been moved out of the work chamber earlier can at the same time be taken off the conveyor device. Thus, at least the entire cycle time required for treatment with the blasting agent on the inside of the work chamber is available for mounting the next untreated workpieces and for removing the workpieces that have previously finished the treatment. Such a method allows for a quasi-continuous, albeit intermittent loading of the workpieces into the work chamber and unloading from there.
So-called rotating satellite tables that protrude from the work chamber with a portion of their peripheral circumferential area and that have multiple mounting devices for workpieces can be used as the conveyor device, for example. The rotating satellite table is turned cyclically by one angle step each time such that a new workpiece arrives in the work chamber while at the same time another one is rotated out of the working chamber. After its removal, at least one space for a new placement of an additional untreated workpiece is available. The problem in this case, however, is shielding the work chamber openings, which are provided for moving the workpieces in and out, from the blasting agents flying about in the working chamber. If the openings are not sealed, then the blasting agents can exit the work chamber unrestricted and can endanger persons and objects in the immediate vicinity due to their high kinetic energy.
If a batch continuously uses the same kind of workpieces, then a partial sealing of the openings can be achieved via so-called template seals, which have an opening that is adapted precisely to the projected contour of the workpiece and through which the workpiece can pass during the cyclical advance. However, even with the template seal, the contour of the opening provided for the passage of the workpiece remains completely free allowing the unrestricted exit of blasting agent from the working chamber.
Blasting agent curtains are also known. In this case, the blasting agent is supplied into a linear funnel above the work chamber opening. The blasting agent exits at the funnel mouth and thus covers the entire area of the opening. The mass of the down-pouring blasting agent veil is so great that it can compensate for the impulse of the blasting agent particles that stem from the turbine wheels or blasting nozzles such that the particles drop down together with the blasting agent veil, where the blasting agent is caught and is returned to the cycle. The continuous turnover of the blasting agent to maintain the veil requires high structural expenditures and, due to the great turned over mass, also needs significant drive energy for the conveyor equipment employed. Also disadvantageous is that outward protruding contours of the workpiece act like an umbrella such that gaps are present in the blasting agent veil underneath, which again allows for blasting agent to exit into the surrounding area.
Known from JP 10328964 A is a work chamber system having a movable separation wall. The separation wall closes an opening for safety reasons but must then be moved to the side for the next angle step of the rotating table. In the particular application presented here, the opening would be exposed and blasting agent would escape at the moment when the plate is moved. Thus, a quasi-continuous operation without interruption of the blasting agent supply is not possible.
DE 198 26 074 C1, originating from the applicant, discloses a work chamber system having one work chamber with loading and unloading in a ring system and sealed via doors. Individual rotating conveyor arms are provided for each workpiece placement location. Since the conveyor arms can be moved individually, workpieces can be moved in and out of the work chamber via interim gates. Although a good seal is achieved at the interim gates, a great effort must be made to drive the individual conveyor arms independently of each other and to seal them in a guide in the work chamber wall.